Abrasive tool comprising bonded abrasive element cemented to supporting element



May 8, 1951 E. E. HOWARD ET AL 2,552,485

ABRASIVE TOOL COMP D ABRASIVE ELEMENT RISING BONDE S CEMENTED T0 SUPPO NG ELEMENTS Filed Jan. 1947 fivenifars ELMER f. HOWARD GEO/P65 J GQE/ FE/PT dehyde had reacted with the phenol.

resin so obtained was vacuum distilled and heat r 3 the bottom .and recesses 13 separated by lands M. The recesses are designed for receiving bonded abrasive elements. Figure 8 shows a side elevation of the ring of Figure 'l in which abrasive elements i5 have been cemented by cement The abrasive tool of Figure 9 comprises a supporting element l l formed by molding and heathardening a mixture of phenolic resin provided with a comminuted fabric filler and provided with an arbor hole [8. An abrasive ring I is cemented to the upper surface of the supporting element by the cement l.

Various features and embodiments of our invention are described in the following examples,

which it is to be understood are for illustrative purposes only and are not limitative.

Example I A cement was prepared by first reacting 343 parts of phenol, 236 parts of a 40% solution of formaldehyde in water and 3.4 parts of sodium hydroxide. The above mixture was heated for approximately 4 hours. At the end of this period substantially all of the formaldehyde had reacted with the phenol. The liquid resin so obtained was vacuum distilled at a pressure of 40-50 mm. until a resin temperature of 90 C. was reached. At the end of this period, the resin was further heated at atmospheric pressure for approximately 45 minutes at 130 C. Alcohol was added to thin the resin to yield a resin solution having a 32% solid content. To 100 parts of the resin solution so prepared were added 260 parts of a 12% alcohol solution of polyvinyl butyral resin designated as XYNC by the Carbide and Carbon Chemicals Corporation and 5 parts of paraformaldehyde. This polyvinyl butyral resin contained approximately 35 parts of butyraldehyde per 100 parts of original resin.

7 Example II A cementwas prepared by first reacting 285 parts of phenol, 165 parts of a solution of formaldehyde in water and 8.6 parts of oxalic.

acid-dihydrate. The above mixture was heated under reflux for approximately 4 hours. At the end of this period substantially all of the formal- The liquid treated in the same way as the alkaline catalyzed liquid resin described in Example I above. At the end of this period alcohol was added to the resin to yield a resin solution having a solid content. To 100 parts of the resin solution so prepared were added 38 parts of a 12% alcohol solution of polyvinyl butyralresin designated as XYNC by the Carbide and Carbon Chemicals Corporation and 7 parts of paraformaldehyde.

' Example III A cresylic acid-phenol formaldehyde resin was prepared by reacting 280 parts of phenol, 120 parts of p cresol, 421 parts of a 40% solution of formaldehyde in water and 8 parts of sodium hydroxide. The above mixture was heated at -60 C. for 24 hours. At the end of this period approximately l-2% of the original amount of formaldehyde added had not reacted. The sodium hydroxide catalyst was then neutralized with dilute acetic acid. The neutral resin was vacuum distilled at a pressure of 30-40 mm. until a resin temperature of approximately 80 C. was reached. 20 parts of p cresol for each 100 parts of resin was added and the mixture was then heated under atmospheric pressure for approximately hour at 140 C. To 100 parts of the resin so obtained were added 2500 parts of a 12% 7 solution of polyvinyl butyral resin of Example I in alcohol. The resulting mixture was used as a cement. 1

Example IV 7 An abrasive tool of the type illustrated in Figures 1 and 2, in which a metal bonded diamond abrasive element was cemented to a backing of a cast aluminum alloy, was prepared as follows:

A backing element 6 inches in diameter and having a width of inch for the surface to which the abrasive ring was to be cemented was cast from an alloy sold commercially by the Frontier Bronze Corporation under the designation Frontier 40 E. The alloy conforms to the ASTM specification for Alloy O, 1326-42'1 and had the following chemical analysis:

Zn, 5.50 Cu, 0.40 Mg, 0.50 Si, 0.30

Cr, 0.50 Mn, 0.30 Ti, 0.20 Al, 91.30 Fe, 1.00

A ring having an outside diameter of 6 inches and an inside diameter of 5 inches to correspond to the mounting surface of the abrasive element was prepared as follows:

A. mixture of metal powders comprising copper and 10% tin was placed in a mold and suitably leveled. This mixture was then partially compacted and the abrasive mix was then placed on top. The abrasive mix comprised diamond particles of grit size and powdered copper and tin powders of similar composition as the non-abrasive portion. The weight of metal powder was roughly '7 times the weight of the diamond abrasive portion. 'After suitable leveling, the metal powder mixture was compacted in the mold at 15 tons pressure per square inch of mold area.

The compacted ring was removed from the mold and sintered at 700 C. for sufficient time to flux the metal powder components and yield a suitable bond for the diamond abrasive. The non-abrasive portion of the ring was roughened on its face prior to cementing. The cement employed was prepared by thinning 37 parts by weight of a liquid composition prepared similarly to that described in Example I but sold commercially by the Bakelite Corporation under the designation XJ 17601 with 32 parts each of acetone and benzol. The resulting cement had a Viscosity of 422 cp. at 25 C. This resin has a ratio of phenol-formaldehyde resin to polyvinyl butyral acetal approximately the same as that of Example III.

Both the abrasive element and the corresponding part of the supporting element were given two thin coats of the cement, allowing 15 minutes for each coat to dry by standing in the air. The abrasive ring was then placed on the supporting element with the adhesive coated surfaces together and the assemblage was hot pressed at a pressure of 300 pounds per square inch, calculated on the area of the cemented surfaces, between steam heated piatens provided with steam under a pressure of 90 pounds (corresponding to 320 F.) for 30 minutes. The steam was then turned oif and cooling water was run into the platens. The assemblage was left in the press until it had cooled to the point where it could be handled by hand Without gloves whereupon the pressure was relieved moved from the mold.

Tests of specially designed test pieces made from the same materials, and according to the practice of this example showed a tensile strength at room temperature in excess of 1500 pounds per square inch and 550 pounds per square inch at a temperature of 300 F. The abrasive element was very strongly attached to the supporting element and the tool was very satisfactory for the purpose intended.

Example V An abrasive tool for grinding the stopper holes in the necks of glass bottles was made of the form illustrated in Figures 3 and 4 with abrasive elements of the type illustrated in Figures 5 and 6.

As illustrated in Figures 3 and 4, the supporting element, which was made of steel, comprised a truncated cone having a length of 1 inch, a diameter at the top of 1 inch, and at the bottom of inch. Three equally spaced recesses inch wide and inch deep were provided along the length of the periphery of the cone which had a driving spindle at the upper or larger end for and the article was remounting the tool in a chuck.

The abrasive elements, which were 1 inch long and 4; inch square, were formed in a manner similar to that described in Example IV except that approximately one-half of the total thickness of 4; inch of the abrasive sticks shown in Figures 5 and 6 consisted of the metal powder without the diamonds (9 of Figures 5 and 6) while the abrasive part It, which was also approximately inch thick, was of a powdered metahdiamond mix of the composition described in Example IV.

The recesses in the supporting element 6 and the metallic portion 9 of the sticks were given two coats of the cement of Example II, drying about 15 minutes after the application of each coat. The abrasive elements were then set into the recesses in the supporting tool, the assemblage was placed in a mold having an inside diameter of 1 inch with the longitudinal axis of the supporting element parallel to that of the hole in the mold. A weight of 5 pounds was then put on the upper fiat surface of the supporting element to press the abrasive elements against the supporting element and the assemblage was put into an oven having a temperature of 320 F. for 30 minutes to heat-harden the resin cement. The assembly was removed and allowed to cool and the completed tool removed. It was found that the abrasive elements were strongly attached to the supporting element and the tool was very satisfactory for the purpose intended.

Example VI A segmental disc wheel adapted for surfacing glass was made according to the design illustrated in Figures '7 and 8. A steel ring of a type sold for use in Blanchard disc grinders and havin an outside diameter of 11 inches and an inside diameter of 9 inches was employed as the supporting element. The upper surface of the ring was provided with recesses inch wide and inch deep which were separated by lands approximately inch long on the inner surface. The recesses were tangential to circles concentric with the ring, the larger one of which was 6 inches in diameter. Metal bonded diamond house 1 inch by /2 inch by inch were pressed as described in Example IV and one surface of. these hones and the recesses of the ring were coated with cement as described in the previous examples.

The abrasive elements were assembled in the recesses in the ring and the assemblage was then hot pressed as described in Example IV. After coating the article was removed from the press and it was found that the abrasive elements were very securely attached to the ring.

Example VII 50 parts by weight, l00 mesh size diamond" bort 3 parts by weight-liquid phenol-formaldehyde resin (sold by The Bakelite Corporation under the designation Bakelite No. XPJ7534) 22 parts by weight--powdered phenol-formaldehyde resin (sold by The-Bakelite Corporation under the designation Bakelite No. BR2428) 25 parts by weight-powdered cryolite filler A ring /4 inch thick and of a diameter to match the supporting element was pressed from this mixture and the article was heated to cure the resin bond.

The mold surface of the abrasive element and theupper surface of thesupporting element were suitably cleaned and coated with two coats of, the cement used in the preceding examples, drying as there described. The abrasive ring was then put on the supporting element and the assemblage was hot pressed at a temperature of 320 F. for 30 minutes. After cooling, it was found that the abrasiveelement wasvery strongly secured to the supporting element and the tool was wholly satisfactory.

Example VIII A resin bonded abrasive disc which contained 35% of 180 grit diamond bort, 25% of a phenolaldehyde resin bond and i0% secondary grain.

and filler was cemented to a steel backing with the cement prepared from the Bakelite resin XJ-1F76011 as described above. A steel disc /2 inch thick and 1 inch in diameter and provided with a threaded spindle having a diameter of /2 inch. was sandblasted to roughen one of the flat surfaces and, after cleaning, that surface was coated with two coats of cement, air drying each coat for about 15 minutes asdescribed;

One of the fiat surfaces of the resin bonded disc was thoroughly cleaned and similarly coated with cement, the elements were assembled and hot pressed as described'in Example IV. After the cement had been cured and the article cooled, it was found that the abrasive element was very strongly attached to the steel backing and that the cement had sufficient toughness and resilience so that the disc withstood very severe abrading operations.

Example IX A diamond hone. was made as follows:

A vitrified. bonded diamond tick 1%, inches long, /;.inch wide and 1%, inch thickwas-made as follows:

.azssasss '71 parts by weight of this mix was then mixed with 29 parts by weight of 220 grit diamond bort and parts of Water to make a moldable mass. A stick was molded from the mix under a pressure of 200-0 pounds per squareinch, and the formed stick was removed from the mold'and fired in a kiln to vitri'fythe bond.

The stick was wet-disked to flatten the surfaces and was then dried for 16 hours at 150 F. and air blasted to clean it off. One of the 1% by /4 inch surfaces was given two coats of the cement, eachof which was air dried for minutes, ,and the abrasive element was then put into a mold 6 inches long by inch wide with the cement surface up. A sufficient quantity of a mixture containing of a 'finely pulverized phenolformaldehyde resin in the A stage and;

80% of granular aluminum of the type known as atomized metal powder and having a particle size such that all of the powder passed through a 100 mesh screen to form a stick /4 inch thick was then put into the mold. The top of the mix was leveled off, a plunger was placed on the mix and the assemblage was hot pressed under a abrasive portion forming the handle was sanded and lacquered. The resulting product was very satisfactory, the abrasive element being strongly .attached to the handle.

The cements employed in making our improved abrasive tools are very strong and tough. They are sufiiciently tacky in the liquid condition :after the solvent has been partially evaporated, :as by air drying for 15 minutes, so that the abrasive elements are held in place strongly enough to permit handling without having the abrasive elements drop off or become displaced with respect to the backing element. This is a decided advantage in making many types of tools such as the bottle neck grinding tool of Example V and the segmental disc of Example VI.

When they are cured, these cements are strongly adherent to various types of supporting elements and bonded abrasives which are commonly used in making many types of tools. They are also very strong and tough and possess suflicient resilience so that they will absorb the stresses occasioned by the difference in coefficient of expansion between the various types of elements and backings and are thus highly resistant to shock. This characteristic makes them very Well suited for many operations where the grinding elements are subjected to shock and the accompanying stresses. This is in marked contrast to the ordinary phenol-formaldehyde resin which The cements are also that. the phenolic constituent sets up to an in fusible condition. Thi property is particularly valuable where. the tools are used without coolant and. are likely to get quite hot.

Various modifications of our invention may be made. The phenol-formaldehyde resin modified by the partial butyraldehyde acetal of polyvinyl alcohol is very well suited for use in our invention but other acetals such as those formed by acetalizing polyvinyl alcohol with formaldehyde and with acetaldehydemay also be used. The acetal does not necessarily have the extent of acetalization described in the specific examples,

although in general we prefer to use rather highly acetalized compounds derived from, polyvinyl alcohol of comparatively high molecular. weight because such compounds have relatively high softening points and do not materially reduce the heat resistance of the phenolic component.

While there may be some reaction between the -a'cetal and-the phenolic resin during the final hyde.

.curing, theliquid cement composition is apparently merely a homogeneous mixture of the phenol-aldehyde liquid resin and the acetal.

with compositions made by both these methods. Although in general we have not found it necessary to use fillers, the cements may be modified by the addition of comminuted fillers such as pulverized cryolite or flint or organic fillers such as cotton flock or wood flour in making some forms of abrasive tools in accordance with our invention.

In the claims where we have referred to an acetal as being acetalized to a certain percentage we mean that the acetal is of such composition that upon hydrolysis it yields that amount of the alde- For example, if 1% parts of acetal are hydrolyzed. and 35 parts of aldehyde are recovered, We would describe that as an acetal which had been acetalized 35%,

While we have described our invention by a number of specific examples, it is to be understood that it is not limited thereto but may be otherwise modified, the scope of theinvention being defined by the appended claims.

We claim:

1. An abrasive tool adapted for both wet and dry grinding comprising a bonded abrasive element attached to a rigid supporting element by a cement comprising the solidified and heat-hardened reaction product of a liquid comprising about parts of a normally liquid phenol-formaldehyde condensation product, about 10-406 parts of a water-insoluble partial acetal of polyvinyl alcohol and an'aldehyde selected from the group consisting of butyraldehyde, formaldehyde and acetaldehyde and a volatile solvent, said cement having the characteristic of air drying to a tacky'ccndition such that the abrasive elements are held in place strongly enough to permit handling without displacement of the said elements with respect to the backing element and in a cured condition being strongly adherent to various types of supporting elements and bonded abrasives, strong enough and of sufficient resilience to absorb the stresses occasioned by the difference in coefficient of the expansion between the abrasive element and the backing and in the use of the tool, highly resistant to shock, and having suflicient heat-resistance to permit use of the tool for dry grinding and sufficient moisture-resistance to withstand the coolants used in wet grinding.

2. An article as claimed in claim 1 wherein the aldehyde of the partial acetal is butyraldehyde.

3. An article as claimed in claim 2 wherein the ratio of the phenol-formaldehyde condensation product to the partial acetal is about 1 to 1-3.

4. An article as claimed in claim 3 wherein the acetal is approximately 35% acetalized and has a molecular weight such that a 7.5% solution of the acetal in alcohol has a viscosity of 250 centipoises at 25 C.

5. An article as claimed in claim 1 wherein the aldehyde of the partial acetal is formaldehyde.

10 6. An article as claimed in claim 1 wherein the aldehyde of the partial acetal is acetaldehyde.

ELMER E. HOWARD, GEORGE J. GOEPFERT.

REFERENCES CITED The following references are of record in'the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Ser. No. 301,165, Putzer-Reybegg (A. P. 0.), published Apr. 20, 1943. 

1. AN ABRASIVE TOOL ADAPTED FOR BOTH WET AND DRY GRINDING COMPRISING A BONDED ABRASIVE ELEMENT ATTACHED TO A RIGID SUPPORTING ELEMENT BY A CEMENT COMPRISING THE SOLIDIFIED AND HEAT-HARDENED REACTION PRODUCT OF A LIQUID PHENOL-FORMALDE100 PARTS OF A NORMALLY LIQUID PHENOL-FORMALDEHYDE CONDENSATION PRODUCT, ABOUT 10-400 PARTS OF A WATER-INSOLUBLE PARTIAL ACETAL OF POLYVINYL ALCOHOL AND AN ALDEHYDE SELECTED FROM THE GROUP CONSISTING OF HUTYRALDEHYDE, FORMALDEHYDE AND ACETALDEHYDE AND A VOLATILE SOLVENT, SAID CEMENT HAVING THE CHARACTERISTIC OF AIR DRYING TO A TACKY CONDITION SUCH THAT THE ABRASIVE ELEMENTS ARE HELD IN PLACE STRONGLY ENOUGH TO PERMIT HANDILING WITHOUT DISPLACEMENTT OF THE SAID ELEMENTS WITH RESPECT TO THE BACKING ELEMENT AND IN A CURED CONDITION BEING STRONGLY ADHERENT TO VARIOUS TYPES OF SUPPORTING ELEMENTS ADHERENT TO VARIABRASIVES, STRONY ENOUGH AND TO SUFFICIENT RESILIENCE TO ABSORB THE STRESSES OCCASIONED BY THE DIFFERENCE IN COEFFICIENT OF THE EXPANSION BETWEEN THE ABRASIVE ELEMENT AND THE BACKING AND IN THE USE OF THE TOOL, HIGHLY RESISTANT TO SHOCK, AND HAVING SUFFICIENT HEAT-RESISTANCE TO PERMIT USE OF THE TOOL FOR DRY GRINDING AND SUFFICIENT MOISTURE-RESISTANCE TO WITHSTAND THE COOLANTS USED IN WET GRINDING. 